My 11-month old son eats food with all these things. The only things we withhold are added salt, added sugar, and honey. Drinks are only milk (currently breastmilk, cows milk in future) and water.
He loves broccoli, sweet potatoes with rosemary, curried courgette, roasted peppers, spinach, bone marrow on toast, shrimp, chicken, lamb, duck, venison, beef, eggs, all kinds of potatoes, leeks, pasta, garlic in everything, cooked onions as garnish, tomatoes, asparagus, hard cheese, cottage cheese, marscapone, cream-based sauces, fruits including blueberries, strawberries, papaya, limes, grapes, watermelon, plums, etc.
So far his only dislikes are cooked apple and yogurt.
My point in all this is that most kids will learn to eat what they're exposed to early and often.
People should not be forced to eat. I absolutely think MIL is in the wrong here, but I also think OP and her children would benefit from working toward a wider palate.